I have a bank of 8 Trojan T105's (the golf cart ones) each of 6v so making up a 48v system. They are almost 5 years old and have worked very hard the last five years as an off-grid power supply to my home. I have no other power source and they have served me well. Currently one of them - the first one in the connection from the panels - seems to not be holding power anymore. The multimeter reading on the others show 13.0 and this one shows 7.0 once the batteries are in use, so that is not good. Some questions: 

Can I do something to help improve it/save it/salvage it to still last me a while? 

Will it help to move this battery elsewhere in the setup? 

Anyone have a second hand T105 they are wanting to sell, otherwise? 

How negatively will this battery affect the other 7 batteries? 

I am heading in the direction of hopefully replacing them with pylontech's but just want them to last me another month or two. 

1 hour ago, Hannah Barnes said:

The multimeter reading on the others show 13.0 and this one shows 7.0 once the batteries are in use, so that is not good

This confuses me. These are 6V batteries, so I would not expect readings of 13V and 7V, unless you are reading across two batteries. What usually happens is one of the batteries lose a cell. When that happens one of two things can happen, it will either read a higher voltage than the rest, or it will read a lower voltage than the rest.

1 hour ago, Hannah Barnes said:

Can I do something to help improve it/save it/salvage it to still last me a while? 

One thing I know about is to add a tiny amount of Epsom salt to the battery. This increases the chemical reactivity and can squeeze a last bit of juice from a battery. Only, I feel very odd about even giving this advice. On youtube you will find several people telling you how to do this, claiming that it revives it completely and saves you thousands. Some even sell you documentation on how to do it (that is always how it works... sell the documentation, so if it doesn't work... it's not your product). It's snake oil. Also, I have no idea how much to use. What I do know is it buys a little extra time. Very little extra time. It's basically good for getting enough juice from an almost-dead car battery to last a few more days, but in a house battery I have no idea.

If the cell has gone dry, sometimes adding water and giving it a good charge can help. If the electrolyte is milky or brown in colour, it's usually over. At least (again), that is my limited experience.

1 hour ago, Hannah Barnes said:

Will it help to move this battery elsewhere in the setup? 

No.

1 hour ago, Hannah Barnes said:

How negatively will this battery affect the other 7 batteries? 

You will run into one of two issues. If the bad battery has an internal short and the voltage remains low (even while charging), the other batteries will end up being overcharged because the voltage divides unevenly due to the bad battery. This will kill them faster. Conversely, if the battery has a high internal resistance, then under charging that battery will show a higher voltage than the rest, and the rest will be undercharged. I don't want to be overly alarmist, but it will affect the others rather quickly, in the space of a week or two. Remember, the others are also long in tooth.

 

Hmm, the first battery you say? I wonder what would cause that?

17 hours ago, plonkster said:

This confuses me. These are 6V batteries, so I would not expect readings of 13V and 7V, unless you are reading across two batteries. What usually happens is one of the batteries lose a cell. When that happens one of two things can happen, it will either read a higher voltage than the rest, or it will read a lower voltage than the rest.

One thing I know about is to add a tiny amount of Epsom salt to the battery. This increases the chemical reactivity and can squeeze a last bit of juice from a battery. Only, I feel very odd about even giving this advice. On youtube you will find several people telling you how to do this, claiming that it revives it completely and saves you thousands. Some even sell you documentation on how to do it (that is always how it works... sell the documentation, so if it doesn't work... it's not your product). It's snake oil. Also, I have no idea how much to use. What I do know is it buys a little extra time. Very little extra time. It's basically good for getting enough juice from an almost-dead car battery to last a few more days, but in a house battery I have no idea.

If the cell has gone dry, sometimes adding water and giving it a good charge can help. If the electrolyte is milky or brown in colour, it's usually over. At least (again), that is my limited experience.

No.

You will run into one of two issues. If the bad battery has an internal short and the voltage remains low (even while charging), the other batteries will end up being overcharged because the voltage divides unevenly due to the bad battery. This will kill them faster. Conversely, if the battery has a high internal resistance, then under charging that battery will show a higher voltage than the rest, and the rest will be undercharged. I don't want to be overly alarmist, but it will affect the others rather quickly, in the space of a week or two. Remember, the others are also long in tooth.

 

Thank you for the help. I had the multimeter on the wrong setting (the joys of not really knowing what you doing but trying to follow internet instructions on testing batteries). I put it on the correct setting and put the borehole pump on which draws 1.5KW. I had 1.1 KW coming in though. Within a few minutes the other 7 batteries were all reading between 6.22 and 6.24 but the first one was reading 5.23 so it is definitely not holding charge. It is really a pity as they others don't seem too bad. This is probably the main reason I will not go with a lead acid battery bank again.....if this happens you basically have to replace the whole set if I understand correctly? 

 

1 minute ago, Hannah Barnes said:

you basically have to replace the whole set if I understand correctly? 

Well, you don't HAVE to, but you kinda have to. If you replace just one battery, it will deteriorate faster because it's dragged down by the the other batteries. And since the others are pretty close to EOL too, it would not be wise.

In the telecoms industry they frequently replace just one cell. But their usage pattern is a bit different. They also tend to buy spare cells and keep them around, so they age with the rest even if not used.

3 hours ago, DeepBass9 said:

Hmm, the first battery you say? I wonder what would cause that?

I wish I knew. They were really doing well lately until I shut down the system for 6 weeks while I was away as there was not anyone to top up the water and they are at that stage where they need water about every 3 weeks. When I started the system up again it was cloudy for about a week so I had to do some charing of batteries with a generator I lent from someone. I am concerned I may have done something when changing the settings that caused this. But I have gone through the setup so many times and cannot see what i might have changed that I did not change back. It may well be my ignorance that is the problem : ) but that is why I went with these batteries 5 years ago. 

I was being somewhat facetious, as there are members on this forum who have stone tablets upon which it is written why there is absolutely no reason for the first battery in a string to behave any differently to the rest!

1 hour ago, DeepBass9 said:

I was being somewhat facetious, as there are members on this forum who have stone tablets upon which it is written why there is absolutely no reason for the first battery in a string to behave any differently to the rest!

Well, that's not really true, it's not that there is no reason at all, of course there is a reason. What I usually protest is the "electrons flows from negative to positive that is why the battery on the negative end goes first" nonsense 🙂

I think the reason the battery at the end fails first, indeed the cell on the end of the battery on the end, is because of larger temperature fluctuations, especially when they are stacked end to end so the middle ones are nicely cushioned in. Over the course of years, it adds up.

My main "proof" of this concept is that in a car, the cell closest to the warm engine tends to go first.